So I drove my '88 to a local mechanic to ask if he would transfer my rear coil springs over to a new set of shocks when they get here since I have no spring compressors. Sitting in his lot is this beautiful white 1990 convertible. Feeling an immediate sense of camaraderie at seeing a similar vintage xjs I ask, "what's the story on that one?"

Turns out the owner tried to clean the engine by spraying it with a garden hose and thereby killed the electrics on top of the engine. He replaced many of the ignition components and when he got it running again he said that the timing chain jumped the cam sprocket on the B bank due to a misfire caused by the hosing of the engine and that the engine is toast. Thats his story anyway..

The owner didn't want anything to do with the car at that point so get this: He signs the pink slip over to the shop and goes out and buys a '96 xjs the next day!

The mechanic didn't want anything to do with it and it was days from being towed to the scrapper. I said I could call a tow truck and have it out of his hair before the scrapper. And the rest is history.

So here I am with this pristine xjs that I picked up for the whopping sum of $0.. I have started her up and true to my suspicions, I don't buy the guys story about it "jumping time". There's no clattering of valves colliding with pistons and the only symptom is that is runs very rough, like to the point where it barely runs; around 200-500 rpm.

So best case scenario I fix it, worst is I use all the beautiful interior pieces for my '88.

Does anyone have any suggestions for where to look first? I want to fix it and it feels like something simple. Tomorrow I'm making sure all the HT leads are hooked up to the right cylinder (gee what if it was THAT easy)

Meanwhile, check out these pics! Merry Christmas to me!

 

I have no experience of Marelli (assuming your car is one), but it is reasonably cheap to do the following and check at each change for improvement: change the crank and flywheel position sensors, maybe? Unplug and clean all connectors in the ignition circuit. Change the ignition HT leads, clean out the dizzy cap, blow-dry out the dizzy internals and fit new plugs, check the loom between the amplifiers and whatever they are connected to. If still is no good, ignition amplifiers, maybe?

All just guesses based on fundamentals, but almost certainly got to be electrical.
Greg

 

Yeah the car's a marelli and I don't have any experience with it either. My '88 is the old lucas system, and this car looks a heck of a lot different under the hood although I understand most of how it works just from years of reading the threads here on the forum. What you said is pretty much along the lines of what I'm gonna do tomorrow- verify that the ignition system is all hooked up properly.

The famous marelli failure where you lose one bank doesn't cause such problems does it? The engine feels like it's fighting with itself; like something is crosswired..

 

Lucky barsteward! How jammy can you get?
Good luck with it.

 

Seriously cool and very lucky.....talk about being in the right place at the right time?

We have to get all the XJS gurus on board with this and get this issue resolved for you.

Can you imagine the mechanics face as you make that trip back there and he sees this XJS in perfect running order

 

My Marelli sits with Gregs.

Look down the LH side of the front of the engine, just below the oil filler cap general area. There is a loom connector there for the front crank sensor, and this has caused a few issues with the 3 Marelli cars I know of here. Unplug it, clean it with Lemon juice, rinse off, reconnect, fired straight up properly.

Same goes for the coil ignitor connectors. They HATE water.

The Marelli rotor rework is a MUST DO.

That car is TOO good to dismantle in anyones language.

The engine does not suffer from the mechanical faults you have been told, so it will be water ingress into some wierd and wonderful area, but you wil find it.

A LARGE bottle af JD, sipped regularly, and work away quietly and carefully.

 

You lucky SOB. I hope its a quick fix for you. Keep us posted.

 

Check how it is fueling too. Obviously it got sat up for electrical reasons though. Make it simple, work your way back from the plug wires until you find where the issue stops, then correct it at that point.

Before you said, "I doubt it" I was already thinking, "A v12 skip the chain, seriously?" haha, nice luck mate

 

Thank you all for the words of encouragement! I thought I'd post a video of the engine running so everyone can understand what I'm dealing with:


I'm still in the process of tracing all the ignition components and making sure nothing is crosswired and course taking all of your advise so far.

Any more ideas of what to look for?

Thanks!
Lou

 

its a shame how mechanics can ruin a cars reputation, general consensus about V12 jags is junk them and be done with them!

i got both my V12 jags for nothing, one 1978 XJS roadster, and other 1975 XJ12C coupe, with MANUAL TRANS!

go figure!! i can't.

 

UPDATE:

The distributor and plugs and the injector harness is wired up correctly. In fact they look new. The HT lead going to the B bank was loose so i popped it in all the way and now the car can actually hold idle! It still is severely misfiring but I can actually just let it sit and it will idle. (very poorly but hey, progress)

BIG NEWS: The LH exhaust is pushing out air very violently and you can definitely feel it missing and stuttering but I can hardly feel anything coming out of The RH exhaust. I think the A bank is dead. Attached is a pic where you can see black soot has been coming from the LH but nothing from the RH side

Thoughts on this?

CLUE: I found two ignition control modules in the passenger footwell. One's hooked up and one is just sitting there. It looks like the mechanic was doing something with it or maybe replaced it since there's two. What does it do? (Pic attached)

 

yup yup. Not familiar with the marelli but it looks like you should be getting zero voltage on half the distributor as it sits

 

jesus dude, how much for the XJC

 

Dude, that's what I've been needing all along! Thanks for that. Any idea what kind of voltage I should be getting out of the power modules?

Is there a *safe* way to see if I'm getting power out of the two ignition coils?

 

Contact me off line, I'll send you my cell, walk you through what I know about Marelli. Been there, done that....

 

Btw, don't start throwing parts at it. Too expensive for maybe a easy fix

 

From the looks of it those are basically just capacitors that can fire whenever he ECU tells them too, I would say look for 12v since it is ahead of the coil but honestly don't know.

If you are just trying to test the coils, the proper way is to disconnect them and measure their resistance to see if it is in spec. Generally the primary is .4-2 ohms and the secondary is 6-15k, but i dont know what the xjs stock coils are specifically

 

Thanks to a long phone call with superchargedtr6 who totally demystified the marelli system for me (again, Thanks Gene!) I had all the info I needed to troubleshoot the ignition system.

After using a spark plug to check for spark though I found that I DO have fire on both sides. I can see the spark plug sparking when it's connected to either bank.

In this video you can see how violent the exhaust is coming out of the B bank exhaust and how weak the bank A exhaust it. You can feel B bank's exhaust standing 5 feet from the back of the car. You can only feel A bank with your hand right up against the tailpipe.

After running the car I observed that the B bank catalytic converter was glowing RED HOT.

SO B bank is blowing supercharged exhaust out the back and cooking the cat and misfiring while who knows what bank A is doing; probably just hanging on for the ride..

Thanks for the continued patience and helpfulness of all on this thread helping me try to save this old girl.


And yes, all that noise is coming from the one side

 

I would be checking the injectors are not gummed up also.
On another note check out this link 1988 Jaguar XJS
, it illustrates the two extremes between the perceived value of these cars over there and over here. Not that I think the seller over here has a hope of getting his asking price.

 

good lord.
So it sounds like the car had an electrical issue on that side, it ran rich like that for long enough to kill the cat, now the cat has collapsed and isn't burning the extra gases. Combination of not doing its job and being damaged is causing secondary explosions in the cat, thus the noise and high pressure.

Thats my guess anyway. I wouldn't run it again until the exhaust is off and you can check that cat out. Sounds like the guy bumped into a small issue and it turned into one bigger than his wallet could handle.